This contract would test the hypothesis that the biostability of thermoplastic polyurethanes (TPU) can be improved by replacing all or part of the (polyether) soft segment with telechelic polydimethylsiloxane (PSX) oligomer during synthesis. This approach is based on the reported improvement in in vivo stability of solvent-cast polyurethanes through the admixture or grafting of reactive PSX into/onto urethane base polymers. In Phase II the in vitro and in vivo stability of ten to fourteen different polyurethanes will be determined. Aromatic TPUs from PSX, polytetramethyleneoxide and polyethyleneoxide and several PSX/polyether terpolymer polyurethane films will be characterized at twelve and eighteen month implantation intervals, by bulk and surface analytical methods capable of detecting molecular weight reduction and changes in surface chemistry and morphology associated with the degradation process. These PSX-TPUs will be suitable for solvent casting, extrusion and injection molding and should combine the biodegradation resistance and desirable surface properties of PSX, with the processing ease and wide range of bulk properties available in conventional TPUs.